Such a method and the apparatus corresponding thereto are known from U.S. Pat. No. 4,827,937. The apparatus has precontrol means, desired value generating means, control means, attenuating means, learning condition recognition means and a learning characteristic field. The precontrol means supplies a precontrol value for the operating variable to be adjusted in dependence upon values of other operating variables than that which is to be adjusted. The desired value generating means supplies a control variable desired value which is compared to a particular control variable actual value. The control means forms an output value in dependence upon the difference between the two mentioned values by means of which the particular precontrol value is corrected in a controlled manner. The precontrol value is however also corrected in a controlled manner with the aid of an adaptation value read out of the learning characteristic field. The learning characteristic field stores adaptation values addressable via values of the address operating variables. For correcting the precontrol values, the learning characteristic field reads out that adaptation value which belongs to the available data record of values of the address operating variables. The adaptation values are always newly determined and always then when the learn condition recognition means issues a learn signal for a particular adaptation value when a predetermined learn condition is fulfilled. The correction occurs with the aid of the output value supplied with the aid of the control means and which is not directly applied for the correction; instead, only after multiplication with a learn intensity factor delivered by the attenuation means.
A learn characteristic field whose support point values are changed with the aid of attenuated values of an actuating variable at the entry of a learn condition is disclosed also in the SAE paper No. 860594, 1986, for an arrangement for adjusting the injection time. With this apparatus, the attenuation means does not continuously give out the same learn intensity value; instead, this value is dependent upon how often learning has taken place at a support point and how large the particular actuating variable is. In order to supply the variable learning intensity values which are factors, the attenuation means includes a counter reading memory and a learn intensity table. In the counter reading memory, a counter reading is stored for each support point of the characteristic field with the support points being identical with those of the learn characteristic field. The reading is increased by 1 up to a 16-bit value with each new learn cycle for each affected support point. However, if the output value for this support point is greater than a threshold value in three sequential learn cycles, the counter reading is reset to 0 for this support point. A learn intensity factor is read out from the learn intensity table in dependence upon the particular counter reading and in dependence upon the particular value of the actuating variable with the learn intensity factor being fixedly predetermined for these address values. The actuating variable is multiplied by this learn intensity factor and the result is added to the previously available support point value.
It has been shown that the system tends to relatively few oscillations when working with a single learn intensity value. The precondition applies however that the value is not set too high. Otherwise, the problem is present that the learning cannot take place with adequate speed if large values of the actuating variable are present.
The invention solves the problem of providing an arrangement for learning control having precontrol for an operating variable of an internal combustion engine which variable is to be adjusted and wherein rapid learning advances are obtained in a learning characteristic field without the control system tending toward oscillations. The invention further solves the problem of providing an apparatus for carrying out such a method.
The method according to the invention is distinguished in that the counter reading in the counter reading memory must no longer be incremented by the value 1 with each learning operation and after three unsatisfactory learning cycles be reset to 0; instead, a counter difference table is provided which stores counter differences in dependence upon the control actuating variable, that is the control deviation, and the already learned advance, that is, the counter reading in the counter reading memory. With these counter differences, the counter reading for a particular operating point in the counter reading memory is incremented or decremented.
According to another embodiment of the invention, the arrangement includes the means already described, that is: precontrol means, desired value generating means, control means, attenuating means which includes a counter reading characteristic field and a learn intensity table, learning condition recognition means and a learning characteristic field. In addition, the arrangement according to the invention includes a counter difference table as part of the attenuating means. This counter difference table stores counter difference values which are addressable via values of counter readings and a quantity dependent upon actuating variables. For each data record of particular values of the counter reading which are present and the quantity dependent upon actuating variables, the arrangement issues the corresponding counter difference value to the counter reading characteristic field to change the counter reading at the particular support point by the counter difference value.
The counter difference table does not increase the counter reading for the particular support point by the fixed value 1 for each learn cycle as in the system according to the above-mentioned SAE-paper; instead, the counter difference is configured so as to be variable. Accordingly, the counter difference value amounts to "+1" only for small values of the actuating variable and small counter difference values. For larger deviations, the difference becomes smaller and passes through the value "0" to negative values. Furthermore, the counter reading values in the counter reading characteristic field are limited to a maximum value. The effect of this measure is the following.
If repeated learning takes place at a support point because of relatively small values of the quantity dependent upon actuating variables, the maximum value for the counter reading is finally reached. This leads to a relatively low learn intensity value whereby the fact is considered that at a point at which already much has been learned, the probability for further large changes is small. If however a large value of the actuating variable dependent quantity occurs for this support point, this means that there is indeed a requirement for a larger learning advance. The counter reading is therefore lowered by several points which leads to an increase in the learn intensity value. The increase is however not so intense as it would be if the counter reading had been reset to 0. This makes evident that the method is variable with reference to the learning speed; however, there is no tendency toward oscillations since no large jump-like changes in the learn intensity values occur.
This advantageous effect can still be supported by a delay step which according to an advantageous development can be introduced additionally. This delay step delays the change of a counter reading in the counter reading characteristic field so long until, after the appearance of a learn signal, first a learn intensity value is read out of the learn intensity table because of the counter reading which is applied before the appearance of the learn signal. If a larger value of the actuating variable dependent quantity occurs, which leads to a relatively intense reduction of the counter reading and thereby to a relatively intense increase of the learn intensity value, the presently available large value of the actuating variable is not attenuated with the new learn intensity value which would lead to a high learn intensity; instead, the large value of the actuating variable is only attenuated with the old learn intensity value which leads to lesser learn intensity. If then no large values of the actuating variable occur any longer for this support point, that is, it appears that a one-time intense deviation case was present, these small values do not lead to too great a change by means of the learning step notwithstanding the increased learn intensity value. If in contrast, the large value of the actuating variable occurs once again or several times again, this is an indication that further large learn steps are required even though at this location much learning has taken place. These learn steps are then also carried out because the new large value of the actuating variable is now attenuated by the learn intensity value increased pursuant to the previous learning step which leads to increased learning intensity. Accordingly, the delay step provides that large learning values are only then issued if large values of actuating variables occur multiple times sequentially. Attention is called to the fact that in the above the statement "large learn intensity value" always means that this value leads to a great learning advance, that is, the value of the actuating variable is only less attenuated than a "small learn intensity value".
As already mentioned, the method of the invention can be used for adjusting the most different operating quantities of an internal combustion engine. However, the application is especially advantageous for adjusting the fuel metering time, especially the injection time. This is so because for systems for adjusting this quantity as control variable, the lambda value is used which is measured in the exhaust gas of the internal combustion engine and which is associated with a considerable dead time between the initiation of a change and the measurement thereof. Such systems tend especially toward oscillations because of the mentioned dead time and the oscillation attenuating measures according to the invention are especially useful.